1. Field of the Invention
The present invention relates to a radio communication apparatus comprising a base unit connected to wired lines and a plurality of radio telephone sets connected to the base unit through a radio link and, more particularly, to a radio communication apparatus which can inform an operator using each individual radio telephone set of service states of the wired lines without a special operation.
2. Description of the Related Art
A conventional apparatus of this kind is arranged as shown in FIG. 11. A base unit 1 is connected to a radio telephone set 2 via a radio link and also to a wired telephone line 3.
The operation of the shown apparatus will be described in outline below.
A signal transmitted over the wired telephone line 3 is applied to a transmitter 5 as a modulating input through a line relay 33 and a hybrid circuit 4. A modulated signal which is produced by the transmitter 5 is transmitted from a transmitting antenna 6 to the radio telephone set 2 in the form of a radio wave.
A radio wave transmitted from the radio telephone set 2 is received by a receiving antenna 7 and demodulated by a receiver 8. The resultant demodulated signal is transmitted to the wired telephone line 3 via the hybrid circuit 4.
A synthesizer 9 outputs a frequency corresponding to a radio channel to the transmitter 5 and the receiver 8.
One output of the receiver 8 is inputted to a received-electric-field detecting circuit 10 for determining its electric field strength. A carrier squelch circuit or a noise squelch circuit may be utilized as the received-electric-field detecting circuit 10.
Another output of the receiver 8 is a data signal which is contained in a demodulated received wave, and is inputted to an identification signal detecting circuit 11 for collating an input signal with an identification signal (ID code) determined by a combination of the base unit 1 and the radio telephone set 2. In the identification signal detecting circuit 11, the other output of the receiver 8 is collated with such an identification signal.
The outputs of the received-electric-field detecting circuit 10 and the identification signal detecting circuit 11 as well as the demodulated output of the data signal from the receiver 8 are inputted to a control circuit 12, where such outputs are used for connection control. The control circuit 12 provides various kinds of controls; for example, it executes radio channel control by controlling the synthesizer 9 or supplies to the transmitter 5 a data signal as a modulating input. An incoming-signal detecting circuit 30 detects a ringing signal of 16 Hz which is received from the wired line at the time of the reception of an incoming call.
The radio telephone set 2 is similarly provided with a receiving antenna 13 and a receiver 14, and a demodulated output is supplied to an earpiece 15. A voice which has been inputted through a mouthpiece 16 is supplied to a transmitter 17 as a modulating input, and a radio wave is transmitted from a transmitting antenna 18.
A synthesizer 19, a received-electric-field detecting circuit 20 and an identification signal detecting signal 21 are substantially identical to those used in the base unit 1, and a control circuit 22 provides control over the radio telephone set 2. A loud speaker 23 serves as a sounder for generating a ringing tone at the time of the reception of an incoming call.
Referring to an electric power circuit, an ac plug 24 of the base unit 1 is connected to a 100 V ac power line, and the output of a rectifying-stabilizing circuit 25 is utilized by individual circuits. The output of the rectifying-stabilizing circuit 25 is also supplied to a rechargeable battery 29 for the radio telephone set 2 via a current controlling resistor 26 and charging terminals 27 and 28. The output of the rechargeable battery 29 is used for the electric power of the radio telephone set 2.
When an incoming signal is received, the above-described conventional example performs control as schematically shown in FIG. 12.
When the incoming-signal detecting circuit 30 detects a ringing signal of 16 Hz transmitted over the wired telephone line 3 during a ready state (Step 34), the base unit 1 sets the frequency of the synthesizer 9 to a control channel and turns on the transmitter 5 to transmit an incoming signal (Step 35). The incoming signal contains a signal for specifying a speech channel (S-CH).
In the meantime, for a predetermined time t1 during the ready state, the radio telephone set 2 holds the synthesizer 19 "on" to set the frequency thereof to a control channel, and holds the receiver 14 "on" (Step 36). If the incoming signal is received during this time (Step 37), the transmitter 17 is turned on (Step 38) to transmit an incoming call response signal (Step 39) and the specified speech channel (S-CH) is selected (Step 45). If the incoming signal is not received during this time, the synthesizer 19 and the receiver 14 are held "off" for a predetermined time t2 (Step 40). The operation of intermittently performing reception while turning on and off the receiver 14 is called "battery saving".
More specifically, if I OFF represents a current consumption occurring when the receiver 14 is off and I ON represents a current consumption occurring when it is on, an average current consumption I A occurring during the ready state is: ##EQU1## Since I ON&gt;&gt;I OFF is normally obtained, I A can be made small.
When the received-electric-field detecting circuit 10 detects a radio wave transmitted from the radio telephone set 2 (Step 41), the base unit 1 stops transmitting the incoming signal (Step 42). If no radio wave is detected at this time, the base unit 1 continues to transmit the incoming signal by a predetermined number of times n (Step 43). The reason why the incoming signal is transmitted by the predetermined number of times n is that the radio telephone set 2 is intermittently performing reception so that it can receive no signal during the time t2. It is sufficient that transmission is continued for a time period which is longer than the time t2 by two signals. The reason why the transmission is performed by n times only is to prevent a control channel from being unnecessarily occupied if, for example, the electric power of the radio telephone set 2 is off or the radio telephone set 2 is excessively remote from the base unit 1.
Then, if the identification signal detecting circuit 11 detects an ID-code coincidence (Step 44), the speech channel S-CH specified by the incoming signal is selected (Step 46). If no ID-code coincidence is found in Step 44, this indicates that a radio telephone set not belonging to this base unit 1 has responded. Accordingly, the base unit 1 waits for the call to disappear from the wired telephone line 3 (Step 57) and returns to the ready state.
After the speech channel S-CH has been selected, the base unit 1 transmits a bell ringing signal (Step 47). When the radio telephone set 2 receives the bell ringing signal (Step 48), the sounder 23 generates a ringing tone (Step 49). If the radio telephone set 2 is set to its off-hook condition in response to the ringing tone (Step 50), an off-hook signal is transmitted (Step 51) and a communication state is established (Step 55).
In the meantime, if the base unit 1 receives the off-hook signal (Step 52), it stops transmitting the bell ringing signal (Step 53) and closes the line relay 33 to form a communication loop with the wired telephone line 3, thereby establishing a communication state (Step 54).
If the number of times of transmission of the incoming signal reaches n, the process proceeds to Step 56, where it is detected whether the reception of the incoming signal has terminated. If the termination of the reception is detected, the base unit 1 returns to the ready state so that it is prevented from again performing an unnecessary receiving operation.
Control which is executed during the originating operation of the radio telephone set 2 is as shown in FIG. 13 in schematic block form. When an originating switch 31 is turned on, origination is initiated (Step 34). The synthesizer 19 is locked on a control channel (C-CH) and the receiver 14 is turned on (Step 35). The received-electric-field detecting circuit 20 checks whether the control channel (C-CH) is idle (Step 36). If the control channel (C-CH) is idle, the transmitter 17 is .turned on and an originating signal (containing an ID code) is transmitted (Step 37).
The base unit 1 receives the originating signal (Step 38), and if an ID-code coincidence is found (Step 39), the transmitter 5 is turned on to transmit a response signal (Step 40). The response signal contains the ID code and the number of the speech channel (S-CH) which has been memorized by the base unit 1 through idle-channel search during the ready state.
The radio telephone set 2 receives a radio wave of the control channel (C-CH) (Step 41), and if an ID-code coincidence is found (Step 42), the speech channel (S-CH) specified by the response signal is selected (Step 43), thereby establishing a communication state.
After the response signal has been transmitted, the base unit 1 also selects the specified speech channel (S-CH) (Step 44) to establish a communication state.
If the radio telephone set 2 does not receive the radio wave of the control channel (C-CH), (for example, if the radio telephone set 2 is excessively remote from the base unit 1), the radio telephone set 2 waits for a predetermined time (Step 45) and generates an alarm sound indicating that connection is impossible (Step 46). Then, the radio telephone set 2 returns to the ready state.
If the above-described radio telephone apparatus is to be applied to a system having a plurality of wired lines, such as a business telephone system, it is necessary Go indicate which wired line is idle.
To meet such necessity, an apparatus which can inform an operator using each individual radio telephone set of the service states of wired lines is disclosed in U.S. patent application Ser. No. 08/150,256 and U.S. Pat. No. 5,218,628 filed by the same applicant.
However, the apparatus disclosed in U.S. patent application Ser. No. 08/150,256 relates to a radio telephone apparatus for a so-called public telephone, and allows a radio telephone set (mobile unit) to display the service states of wired lines only when a request for origination from the mobile unit is not accepted. Accordingly, the disclosed apparatus differs from a business-telephone type radio communication apparatus to which the present invention is directed.
The apparatus disclosed in U.S. Pat. No. 5,218,628 has an arrangement in which a base unit transmits information indicative of the service states of wired lines in response to a request from a mobile unit and the mobile unit displays the service states of the wired lines on the basis of the information. With such an arrangement, it is necessary for the operator using the mobile unit to perform a special operation in order to be informed of the service states of the wired lines. As a result, the arrangement forces the operator to perform an extremely complicated operation. It is, therefore, disadvantageous to apply such an apparatus to the business-telephone type radio communication apparatus to which the present invention is directed.
In other words, in the case of the business-telephone type radio communication apparatus to which the present invention is directed, it is preferable that the operator can always be informed of the service states of the wired lines without performing a special operation when using each individual radio telephone set.
However, as described above, to reduce a current consumption and to effectively utilize radio waves, when the radio telephone sets are in their ready states, the transmission of each set is shut off and no radio link is established. Accordingly, to realize an arrangement which can inform the operator using each individual radio telephone set of the service states of the wired lines without a special operation, it is important to consider how to transmit information indicative of the service states of the wired lines to all radio telephone sets.